1. Field of the Invention
The present invention relates to an indirect radial ray detector and a method for manufacturing the same.
2. Description of the Related Art
As new-generation image detectors for X-ray diagnosis, an attention has been paid to planar-shaped X-ray detectors using an active matrix or a solid-state image sensing device such as CCD or CMOS. When such X-ray detectors are irradiated with X-rays, X-ray photographed images or real-time X-ray images are output as digital signals. Since the X-ray detectors are solid-state detectors, they are greatly expected from viewpoints of image quality performance and stability, and thus considerable research and development are being promoted.
The X-ray detectors using active matrix are developed mainly for photographing chest regions to collect still images with comparatively large radiation dosage and general photographing, and have been commodified in recent years. The commodification of the X-ray detectors are assumed in the near feature in order to apply them to the fields of circulatory organs and digestive organs in which real-time moving images of not less than 30 frames per second at transmitted ray amount should be realized with higher performance. In the application to the moving images, improvement of the signal-to-noise ratio and a real-time processing technique for very small signals become important terms of the development.
The X-ray detectors using solid-state image sensing device such as CCD or CMOS have been commodified in recent years for nondestructive inspection in the industrial field where still images are collected at large radiation dosage or dentistry where the detectors are put into mouth capsules and still images are collected. In such X-ray detectors, the improvement of the signal-to-noise ratio and the real-time process for very small signals, miniaturization of the X-ray detectors, and improvement of reliability as well as the application to moving images are important terms of the development.
The X-ray detectors are roughly classified into two systems including a direct system and an indirect system. The direct system is a system which converts X-rays directly into a charge signal by means of a photoconductive film made of a-Se or the like. On the other hand, the indirect system is a system which once converts X-rays into visible light by means of a scintillation layer and then converts the visible light into a signal charge by means of an a-Si photodiode, CCD or CMOS.
In the conventional indirect X-ray detectors, as shown in FIG. 4, a light receiving section 2 having a plurality of photoelectric conversion elements 2a for converting visible light into an electric signal is formed on a photoelectric conversion substrate 1, and substrate-side electrode pads 3 which are electrically connected to the photoelectric conversion elements 2a, respectively, are formed outside the light receiving section 2. A scintillation layer 4 which converts X-rays into visible light is formed on the light receiving section 2 of the photoelectric conversion substrate 1, and a reflection layer 5 which heightens use efficiency of the converted visible light is formed on the scintillation layer 4.
The photoelectric conversion substrate 1 is fixed onto a base 7 having base-side electrode pads 6 for external connection, and the substrate-side electrode pads 3 and the base-side electrode pads 6 are electrically connected by interconnects 8. The substrate-side electrode pads 3, the base-side electrode pads 6 and the interconnects 8 are coated with a protective layer 9 composed mainly of a resin material in order to achieve reliability of the X-ray detectors. In order to protect the scintillation layer 4, the surfaces of the scintillation layer 4 and the reflection layer 5 are coated with a protective layer, not shown, and a protective cover, not shown, is provided to an opening of the base 7 so that the inside of the base 7 is sealed.
Normally, in the indirect X-ray detectors, the property of the scintillation layer is structurally important, and high-luminance fluorescent materials composed of a halogen compound such as CsI or an oxide compound such as GOS are mostly used as the scintillation layer in order to improve output signal intensity with respect to incident X-ray. Further, in general, a high-density scintillation layer is often formed uniformly on a photoelectric conversion substrate according to a vapor growth method such as a vacuum deposition method, a sputtering method and a CVD method.
However, when the halogen compound such as CsI as the high-luminance fluorescent material is used for the scintillation layer, reactivity of a halogen element such as iodine is high, and thus the scintillation layer reacts with electropositive elements in the photoelectric conversion elements, the substrate-side electrode pads, the base-side electrode pads and the interconnects for electrically connecting these pads in contact with the scintillation layer. As a result, the photoelectric conversion elements and the like are corroded, and thus various properties and reliability of the X-ray detectors deteriorate.
As shown in FIG. 4, the substrate-side electrode pads 3, the base-side electrode pads 6 and the interconnects 8 for electrically connecting these pads 3 and 6 are coated with the protective layer 9, so that the corrosion can be prevented. Since the protective layer 9 is made mainly of a resin material, its X-ray absorptance is lower than that of the scintillation layer 4, and thus the reliability might deteriorate as a result of X-ray resistance.
On the other hand, as to the photoelectric conversion elements, although the indirect X-ray detectors reduces interlayer peeling of the scintillation layer, a transparent layer made of polyimide or the like is formed on the surface of the light receiving section of the photoelectric conversion substrate, and the scintillation layer is formed on the transparent layer so that the corrosion can be prevented (for example, see page 3 and FIG. 1 in Jpn. Pat. Appln. KOKAI Publication No. 2001-188086).